Study On The Change Of Taste Compounds During The Processing And The Isolation And Identification Of Flavour Peptides In Water Boild Salted Duck

Water boiled salted duck is one of the low temperature cooked meat products in traditional Chinese meat products. It is famous for its delicate processing, savoury, and tender flavour. In resent years, modern industrial processing method has been applied in water boiled salted duck instead of the traditional manual workshop-based manufacture. Dry-curing, brining, cold storage and boiling are the main process in industrial production, which also make a great contribution to the flavor of ducks.The aim of this research is to investigate the effects of process on the taste of water boiled salted duck meat and clarify the key flavour peptides that account for the delicious taste, so as to provide a theory basis for studying and accommodating the flavor, improving the processing technology of water boiled salted duck. The contents and results are as follows.1. The change of taste compounds and taste properties of water-boiled salted duck during the processingDuring the processing of water-boiled salted duck, the water content of duck showed a decrease tendency during the processing. The protein content had no significant changes before the process of boiling, but largely increased during the boiling. The lower pH value and suitable salt content of water-boiled salted duck were largely contributed to the saltness and umami sensory property.The main taste compounds of water-boiled salted duck during processing, including nucleotides and related compounds, free amino acids were analyzed by high performance liquid chromatography(HPLC) and amino acid auto-analyzer. Furthermore, taste impact of the main taste compounds was evaluated by taste active values (TAVs) methods; umami intensity of water-boiled salted duck was evaluated by equivalent umami concentration (EUC) methods. Results showed that the special processes, brining and boiling, produced an increasing effect on the taste compounds, which could be the reason for the savoury taste of water-boiled salted duck.5’-Ionosine-monophosphate(5’-IMP) and Inosine(Ⅰ) were the major nucleotides, accounting for 47.33% of the total nucleotides and related compounds. Taurine(212.37 mg·100-1·g-1), Glutamic acid(96.66 mg·100-1·g-1) and Alanine(95.52 mg·100-1·g-1) were the major free amino acids. The TAV values of 5’-IMP and glutamic acid were greater than one, and they had strong taste impacts on the duck meat flavour. The EUC was 3.89 g MSG·100·g-1 duck meat, which meant that the umami taste of water-boiled salted duck was very intense.The taste properties of water-boiled salted duck during processing, including saltiness, umami, sourness, bitterness, astringency and richness were detected by TS-5000Z taste analysis system. Results showed that saltiness of water-boiled salted duck changed most significantly during the processing, it continuously increased during dry-curing, brining and cold storage, but significantly decreased during the boiling. The umami taste of raw duck was the most intense, and it significantly decreased before the process of boiling, but largely increased during the boiling. Richness had no significant changes before cold storage, but significantly increased during the cold storage and boiling. The bad taste properties, sourness, bitterness and astringency showed a decrease tendency during the processing.2. Isolation and identification of flavour peptides from water-boiled salted duckTo clarify the key flavour peptides that account for the savoury taste of water-boiled salted duck, this study was performed to examine flavour peptides extracted from the meat of water-boiled salted duck. Peptides fractions (F1, F2, F3, F4 and F5) were purified from an aqueous extract of duck muscle by ultrafiltration and Sephadex G-15 gel filtration chromatography. Fraction F1 was identified to have the most intense taste through sensory evaluation analysis and electronic tongue determination. Totally 7 peptides in F1 fraction were further separated and identified by Nano-LC-ESI LTQ-Orbitrap MS/MS. Three key flavour peptides were identified as Gly-Pro-Asp-Pro-Leu-Arg-Tyr-Met(GPDPLRYM), Asp-Pro-Leu-Arg-Tyr-Met(DPLRYM)and Val-Val-Thr-Asn-Pro-Ser-Arg-Pro-Trp(VVTN PSRPW) for the higher ALC% and signal strength of peptide ions.The three identified peptides were synthesized by solid-phase synthesis, named F1T3, F1T5 and F1T7, respectively. The taste properties of three synthesized peptides were evaluated by electronic tongue. The taste location between F1T3 and Fl was the closest followed by F1T3 and ultrafiltration fraction (F). This suggested that F1T3 had a similar taste with the total extract from water-boiled salted duck. For taste, F1T3 was close to umami, while F1T5 and F1T7 were close to saltness. The results showed that these three key flavour peptides could be important components of the savoury taste of Nanjing cooked duck.